DENVER (AP) — Democratic U.S. Sen. Mark Udall is about even with his expected Republican challenger, U.S. Rep. Cory Gardner, according to a poll released Thursday that confirms Colorado’s Senate race is one of the nation’s most competitive.

The Quinnipiac University poll shows Udall has the support of 45 percent of voters, compared with Gardner’s 44 percent. That’s well within the poll’s margin of error of plus or minus 2.7 percentage points.

Colorado’s Senate race is expected to be one of the most expensive in the nation. Republicans need to gain six seats to take back the Senate, and Gardner’s entry at the end of February put Udall’s seat in play.

The poll found that each candidate has the backing of 9 out of 10 voters from their respective parties. They are nearly evenly split among independent voters, with a 43 percent to 41 percent edge for Gardner.

Voters were evenly divided on Udall’s job performance. The economy and health care topped issues important to voters, the poll found.

“In a race that is both too close to call and one of the prime targets for Republicans trying to take back the Senate, Colorado Sen. Mark Udall might best focus on one predominant concern – the economy,” said Tim Malloy, assistant director of the poll.

Udall instead aired his first ad this week attacking Gardner for his anti-abortion-rights stance. It’s a tactic out of the Democratic playbook in a state where most elections are decided by a small number of women who are either political independents or socially moderate Republicans.

Udall, a first-term incumbent, is being dragged down by President Barack Obama, who is viewed unfavorably by 59 percent of voters surveyed, according to the poll. An identical percentage of voters have negative views of the Affordable Care Act.

The telephone poll of 1,298 registered voters was conducted April 15-21.